The strangers—that is, the aliens, the non-Israelite population of the land (compare to 2 Chronicles 2:17).

David gathers craftsmen and accumulates materials for building the house of God.

And David commanded to gather together the strangers that were in the land of Israel; and he set masons to hew wrought stones to build the hous…

And David commanded to gather together the strangers that were
in the land of Israel
…

Following the terrible judgment inflicted on Israel for David's sin, God pointed out the place where he wanted the temple to be built. After this, …